1. Field of the Invention
The present invention relates to measuring and positioning machines for orienting workpieces and, more particularly, to self-centering automatic coordinate measuring forms of such machines.
2. Description of the Prior Art
Rapid, zero-positioned measuring machines are currently widely distributed. However, such machines show two significant flaws. First is the problem of centering the boreholes to be measured. Second is the problem of setting the coordinate zero line for the object to be measured.
In conventional prior art measuring machines, measuring rolls are utilized for measuring distances of axes to center boreholes. In order that the roller-cone employed can be kept as small as possible, its measuring cone is of very elongated form. For boreholes or rack-holes which are non-continuous, such measuring cones, in most cases, are not able to adequately perform the measuring work. Furthermore, such measuring cones are only able to contact the edge of the hole or the hole facets. However, hole facets are generally imprecisely worked. It therefore is impossible to perform precise centering with this type prior art method. In expensive measuring-machines, the centering of the borehole is achieved by scanning the walls of the borehole using star-scanners and the center location is established and held by means of a computer. This method, however, is very complicated and costly.
The art has not yet provided a direct solution for automatically adjusting the initial zero line of a piece to be measured to that of the measuring axis of the coordinate table. Most workpieces have no precise-measuring stop line. In general, the workpiece is placed in a more or less (that is angularly offset) position on the measuring table. One first locates an initial zero point and then locates a second reference point or a reference line which should be parallel to the measuring axis. This is either manually accomplished or is done by means of knocking the workpiece, which is very difficult and time-consuming. This is because once the measuring spindle has been adjusted to the initial point of the workpiece, it must be moved away therefrom in order to locate the second reference point or reference line. When this happens, the released initial point can thereby again be displaced. Thus, the adjusting phase develops into a forward and backward motion as a result of which it is very difficult to obtain satisfactory precisioning. Moreover, should there develop an error in locating the initial line of the workpiece relative to the measuring axis of the measuring table, then the entire measuring becomes illusory. In expensive measuring machines, the workpieces may be placed at any tilted angle onto the measuring table. However, the tilted angle is established by a computer by means of two reference points and the entire mis-measurement can be computed and corrected on a trigonometric basis. Nevertheless, to correct these consciously-made wrong measurements in toto is basically illogical and such methods do not represent a direct or satisfactory ideal solution. Aside from the involved handling, which is not secure from errors by untrained persons, the most compelling disadvantage is that it is economically prohibitive to utilize a computer in relation to this simple measuring task.